As if one plague wasn鈥檛 enough. The dreaded chytrid fungus is already sweeping through the world鈥檚 amphibians. Now, to add to their woes, it seems that two lethal viruses have devastated several amphibian populations in Spain.
The impact is not pretty. 鈥淭hey haemorrhage throughout their tissues, vomit blood and pass it out through their guts, and suffer huge open ulcers,鈥� says Stephen Price of University College London. Loss of limbs can also result from infection by these ranaviruses.
Ranaviruses have been seen in Europe, including France, the Netherlands and Belgium, for a while, but a study by Price and his colleagues is the first to show what just how devastating they can be for amphibian populations. They recorded the simultaneous collapse of three species that succumbed to ranaviruses in Spain鈥檚 National Park. 鈥淲e saw declines ranging from 60 to almost 100 per cent in all three species.鈥� The viral outbreaks have occurred since 2005, in several distant sites across the park.
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Prior to the work, ranaviruses had only been seen each to have such severe effects in a single host species. But the team鈥檚 study shows that three main species have been struck down by the ranaviruses 鈥� the common midwife toad (Alytes obstetricans), the alpine newt (Ichthyosaura alpestris) and the common toad (Bufo bufo). Price says all six amphibian species native to the most species-rich site in the park have now been infected. Thankfully, he says, the viruses have not yet overlapped anywhere with the chytrid fungus, which has devastated amphibian populations globally.
One of the ranaviruses that stuck Picos de Europa was the common midwife toad ranavirus (CMTV). The other, the Bosca鈥檚 newt virus (BNV), also infected and killed a snake that ate an infected amphibian, suggesting that the virus may also threaten reptiles.
Tracking the virus
Price is now gathering more samples from throughout the world. He plans to build a viral family tree to show how the ranaviruses found in Spain got there. The specific genetic strains that struck the park鈥檚 amphibians have never been identified before. One theory is that the virus may have arrived in Spain in amphibians imported from China, where species like bullfrogs are farmed for food.
鈥淭he global trade in amphibians has been implicated as a key mechanism that is vectoring amphibian pathogens worldwide, leading to losses of biodiversity in naive populations and species,鈥� says of Imperial College London. 鈥淭his research on CMTV-like viruses shows that, while we don鈥檛 know the vector in this case, we need to be acutely aware that our borders are not biosecure to these pathogens,鈥� he says. Cooperation with the amphibian trade is needed to stop more spreading of diseases through infected imports, he adds.
By finding out more about the origins of the viruses and which species they most prefer, Price hopes to find ways of keeping the virus in check. 鈥淭he problem is that we don鈥檛 know where the viruses are spread or moving,鈥� he says.
Clarification, 18 October, 2014: The specificity of ranaviruses has been clarified since this article was first published.
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